1. Technical Field
This disclosure generally relates to the front-projection screens and more specifically relates to front projection screens that optimally manage the diffusion of light such that polarization is preserved. Such screens may additionally maximize image brightness and contrast subject to specific projector and observation angles.
2. Background
In stereoscopic 3D systems utilizing passive polarization analyzing eyewear, the screen is an integral part of the system. Any depolarization occurring at the screen results in cross-talk, where the image intended for one eye is partially transmitted to the opposite eye. This cross-talk is manifested as a “ghost image,” which erodes the quality of the experience and creates eye fatigue. As such, it is desirable to provide extremely low cross-talk under the most extreme illumination and observation angular conditions.
Known front-projection screens, such as those used in the 2D cinema, are virtual Lambertian scatterers. Owing to the statistics of the surface roughness of such known screens, they have very poor polarization preservation and poor effective light efficiency (i.e., while total integrated scatter, or TIS, is high, utilization of light in angle space is poor).
A known technique for providing stereoscopic 3D polarization preserving screens is to spray-paint aluminum flake in a transparent binder onto a PVC substrate. Such statistical surfaces provide limited control of screen gain profile, directionality, and polarization. Moreover, coating processes frequently show resolvable structures (e.g. sparkle), and uniformity problems, such as textures. Such “silver screens” are frequently delicate, and are not able to withstand a mild abrasive cleaning process.
Lambertian screens provide uniform appearance in observed brightness, but make poor use of projection light. That is, a significant portion of incident light is scattered outside of the field of view, reducing system efficiency. Moreover, a portion of scattered light is directed back to the screen, reducing contrast and color saturation.
Accordingly, there is a need for a front projection screen which is engineered to optimally disperse light into a range of observation angles, such that the input state of polarization is accurately preserved.